GAN group crystal base member having low dislocation density, use thereof and manufacturing methods thereof

ABSTRACT

A GaN group crystal base member comprising a base substrate, a mask layer partially covering the surface of said base substrate to give a masked region, and a GaN group crystal layer grown thereon to cover the mask layer, which is partially in direct contact with the non-masked region of the base substrate, use thereof for a semiconductor element, manufacturing methods thereof and a method for controlling a dislocation line. The manufacturing method of the present invention is capable of making a part in the GaN group crystal layer, which is above a masked region or non-masked region, have a low dislocation density.

FIELD OF THE INVENTION

The present invention relates to a GaN (gallium nitride) group crystalbase member, use thereof (e.g., semiconductor light emitting element),and manufacturing methods thereof.

BACKGROUND OF THE INVENTION

A conventional method for crystal growth of a GaN semiconductor materialto give a thick film generally comprises forming a buffer layer of ZnOand the like on a sapphire substrate and growing a GaN semiconductormaterial by an HVPE method. An improved technique thereof involves theuse of a substrate such as one made from spinel, LGO, LAO, ZnO, SiC andthe like or a substrate showing easy cleavage performance, instead ofthe sapphire substrate.

However, the crystal growth of a GaN semiconductor material to give athick film results in tremendous amounts of stress applied on theinterface between GaN and sapphire substrate due to different latticeconstants and coefficients of thermal expansion, which in turn leads toa problem in that GaN is broken and a bulky substrate cannot beobtained. In addition, this method produces only a substrate having anextremely great dislocation density (e.g., 1×10⁹ cm⁻²-1×10¹⁰ cm⁻²). Bydislocation is meant here a defect that occurs when a semiconductorlayer is grown on a substrate under a lattice mismatch. The dislocationthus created advances upward along with the growth of the crystal layerand passes through an active layer to form a continuous defectiveportion called a dislocation line (continuous dislocation). Inasmuch asthis dislocation is a crystal defect, it acts as a non-radiativerecombination center or as a path of a current to ultimately inducecurrent leakage when such GaN semiconductor material is used for a lightemitting element, which in turn degrades light emitting performance andshortens the service life.

It is therefore an object of the present invention to provide a GaNgroup crystal base member having a low dislocation density.

Another object of the present invention is to provide use of theaforementioned GaN group crystal base member.

Yet another object of the present invention is to provide a method forproducing the aforementioned GaN group crystal base member and a methodfor producing a light emitting element which is one use thereof.

SUMMARY OF THE INVENTION

The GaN group crystal base member of the present invention comprises abase substrate, a mask layer partially covering the surface of said basesubstrate, and a GaN group crystal layer which is grown thereon to coverthe above-mentioned mask layer and which is partially in direct contactwith the non-masked region of the base substrate. Said base substrateallows growth of a GaN group crystal in the C axis orientation as thethickness direction, and the mask layer is made from a materialsubstantially free from GaN group crystal growth.

The base substrate partially covered with a mask layer is hereinaftersimply called a “substrate for growth” to mean a substrate used to growa GaN group crystal The GaN group crystal layer grows from thenon-masked region of the substrate for growth as the staring point untilit covers the mask layer, whereby a GaN group crystal base membercomprising the base substrate, mask layer and GaN group crystal layer isprovided.

The method for manufacturing the GaN group crystal base member of thepresent invention comprises partially covering the surface of the basesubstrate with a mask layer made from a material substantially free fromcrystal growth, and then growing a GaN group crystal layer from thenon-masked region on the base substrate surface as the starting point toa thickness sufficient to cover said mask layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a), (b) are sectional views of the GaN group crystal base memberof the present invention and its state during the ongoing growth.

FIG. 2 shows one embodiment of the mask layer pattern used in thepresent invention.

FIG. 3 is a sectional view of a conventional GaN group crystal basemember.

FIG. 4 is a sectional view of another embodiment of the GaN groupcrystal base member of the present invention.

FIGS. 5(a), (b) show one embodiment of the substrate for growth to beused in the present invention.

FIG. 6 shows one embodiment of the substrate for growth to be used inthe present invention and the arrangement pattern of the openings on themask layer.

FIG. 7 shows the effect of the arrangement pattern of the openings inthe present invention.

FIGS. 8(a), (b) show the growth of the crystal in the transversedirection from the openings in the present invention, wherein FIG. 8(a)shows the growth of a GaN group crystal in the transverse direction fromone square opening (two-dot chain line) shown in FIG. 1 and FIG. 8(b)shows merger of GaN group crystals from four directions into one.

FIGS. 9(a), (b) show the production steps of a GaN group light emittingdiode using the substrate for growth of the present invention.

FIGS. 10(a)-(c) show examples of the width of the element and the widthof the active part thereof.

FIG. 11 is a perspective view showing the GaN group stripe lasers duringproduction using the substrate for growth of the present invention,wherein the dotted lines on the both ends of the drawing are break linesand electrodes are omitted.

FIGS. 12(a)-(c) show a method for controlling the dislocation lineaccording to the present invention and one embodiment of themanufacturing method of the GaN group crystal base member of the presentinvention.

FIGS. 13(a)-(c) show another method for controlling the dislocation lineaccording to the present invention and another embodiment of themanufacturing method of the GaN group crystal base member of the presentinvention.

FIG. 14 shows one embodiment of the GaN group light emitting elementobtained by the method of FIG. 12.

FIG. 15 shows one embodiment of the GaN group light emitting elementobtained by the method of FIG. 13.

FIG. 16 shows one embodiment of the structure of the GaN group crystalbase member obtained by the manufacturing method of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

In the present specification, when the lattice plane of a crystal havinga hexagonal system, such as GaN group crystal and sapphire substrate, isindicated by four Miller indices (h, k, i, l) and the index is in thenegative, a minus symbol is put in front of the index. Other than theminus symbol indication, the widely accepted indication of Millerindices will be employed. In the case of GaN group crystals, forexample, there are six prism planes (specific planes) parallel to the Caxis. One of them is indicated as (1-100), and when the six planes areto be equivalently indicated, the symbol {1-100} will be used. Theplanes perpendicular to the above-mentioned {1-100} plane and parallelto the C axis are equivalently designated as {11-20}. The orientationperpendicular to the (1-100) plane is designated as [1-100] and theorientation collectively equivalent thereto is designated as <1-100>.The orientation perpendicular to the (11-20) plane is designated as[11-20] and the orientation collectively equivalent thereto isdesignated as <11-20>. When the Miller indices are to be shown in thedrawings and the index is in the negative, the index is supplied with abar on the index numeral and other indications follow those of Millerindices. The crystal orientation as used in the present invention is theorientation based on the GaN group crystal grown on the base substratein the C axis orientation as the thickness direction.

The non-dislocation as referred to in the present invention means notonly the ideal state completely free of dislocation which istheoretically possible, but also the state considered to havesufficiently low dislocation density to the degree the influence of thedislocation may be ignored from the industrial aspect, when compared tothe dislocation density in the case where a GaN group crystal is grownon a sapphire substrate via a buffer layer.

The GaN group as referred to in the present invention means a materialof the formula: In_(x)Ga_(x)Al_(z)N (0≦X1, 0≦Y≦1, 0≦Z≦1, X+Y+Z=1). Inparticular, the material useful as a thick film layer includes thosemade from GaN, AlGaN, InGaN and the like.

The present inventors previously proposed forming mask layers 2 having alattice pattern on a base substrate I to avoid cracks in the GaN layercaused by the different lattice constants as well as differentcoefficients of thermal expansion between GaN and sapphire substrate,and growing chip sized GaN layers 30 in the openings (non-masked region)exposing the substrate surface, as shown in FIG. 3 (Japanese PatentUnexamined Publication No. 273367/1995).

Subsequent studies done by the present inventors have revealed that,when the disposed GaN layers 30 are further grown, the crystal grows notonly in the thickness direction but also in the transverse directionfrom each GaN layer 30 onto the mask layer 2, as shown in FIG. 1(a). Ithas been further clarified that different growth conditions result incrystal orientation-dependent crystal growth.

It has been further found that the dislocation present in theabove-mentioned crystals may continue from the base inclusive of thesubstrate or may be generated in certain growth interface and grow alongwith the crystal growth. When GaN crystal is grown from the non-maskedregion as the starting point to cover the mask layer, the thicknessnecessary to cover the mask layer and the location of the lowdislocation density part vary according to the direction of the masklayer (direction of the boundary line between the masked region andnon-masked region) and atmospheric gas during GaN crystal growth.

When the above-mentioned transverse growth further proceeds, as shown inFIG. 1 (b), the mask layer 2 is completely embedded, and a bulky, thickGaN layer 3 which is flat and associated with no cracks and less defectscan be obtained. It is speculated that the absence of cracks isattributable to the alleviation of the stress resulting from the factthat the mask layer 2 and GaN layer 3 are merely in contact with eachother at the interface between them. The present invention is based onthese findings.

In the GaN group crystal base member of the present invention as shownin the embodiment of FIG. 1, the surface of the base substrate 1 ispartially covered by mask layer 2, and the GaN group crystal layer 3grows from the non-masked region 11 of the base substrate 1 and coversthe mask layer 2.

The material of the above-mentioned base substrate 1 may be, forexample, sapphire crystal (C face, A face), rock crystal, SiC and thelike which are widely used to form GaN group crystal layers. Inparticular, sapphire substrate (C face) is preferred. The substrate mayhave a buffer layer of ZnO, MgO, AlN and the like on its surface toreduce the difference in the lattice constant and coefficient of thermalexpansion between the substrate and GaN group crystal layer. Inaddition, a material having a thin layer of In_(x)Ga_(y)Al_(z)N (0≦X≦1,0≦Y≦1, 0≦Z≦1, X+Y+Z=1) such as GaN or GaAlN formed on said buffer layermay be appropriately used. Such base substrate can reduce the density ofthe dislocation newly generated from the non-masked region into a GaNgroup crystal layer 3 and afford a GaN group crystal layer 3 having finecrystallinity.

The mask layer 2 should be one, from which surface a GaN group crystaldoes not substantially grow. Examples of such material includenon-crystalline materials such as nitrides and oxides of Si, Ti, Ta, Zrand the like, namely, SiO₂, SiN_(x)SiO_(1−x)N_(x), TiO₂, ZrO₂ and thelike. In particular, SiO₂, SiN_(x) and SiO_(1−x)N_(x) are suitable whichare superior in heat resistance and which allow relatively easy filmformation and removal by etching. These materials may be formed into amultilayer structure.

The mask layer 2 may be formed by either an additive method orsubtractive method. The subtractive method may comprise covering theentire substrate with a masking material by MOVPE, sputtering, CVD andthe like and leaving a desired pattern by etching, thereby exposing thesubstrate surface to be used as a non-masked region.

The mask layer 2 may have any pattern such as a lattice pattern, astripe pattern and a dot pattern. Of these, a lattice pattern ispreferable in that it enables efficient use of the surface area of thebase substrate 1. When the mask layer is formed into a lattice pattern,the shape of one exposed part (non-masked region) may be a quadrangle, apolygon or a circle.

The present inventors have found that the rate of GaN group crystalgrowth in the transverse direction on the mask layer is greater in thegrowth in the <11-20> orientation than in the growth in the <1-100>orientation. As shown in FIG. 2, it is desirable that this property beutilized to the maximum possible extent by setting the relation betweenthe lattice width A in the <11-20> orientation and the lattice width Bin the <1-100> orientation to 0≦A≦B. The widths A, B of the lattice arepreferably about 1 μm to 2 mm. When the shape of the exposed part isquadrangle, it is an about 1 μm to 2 mm quadrangle.

A GaN group crystal layer 3 is formed on the substrate for growth. Thegrowth of the GaN group crystal starts from the non-masked region aloneof the base substrate 1. In other words, the GaN group crystal layer 3and the base substrate 1 directly contact with each other only at thenon-masked region. Further growth completely buries the cavity as thenon-masked region, and the top surface of the crystal becomes higherthan the top surface of the mask layer 2. Yet further growth makes theGaN group crystal extend not only in the thickness direction but also inthe transverse direction along the top surface of the mask layer, whichin due course joins the crystals which have grown from differentnon-masked regions as starting points. The crystal ultimately covers themask layer 2 completely, along which the growth in the thicknessdirection continues until it forms the GaN group crystal layer 3.

The GaN group crystal layer 3 can be grown by any method such as theHVPE method, the MOCVD method, the MBE method and the like. When a thickfilm is to be grown in the C axis orientation at a high speed, the HVPEmethod is preferable, but when a thin film is to be formed, the MOCVDmethod is preferable.

A semiconductor light emitting element such as LED and LD (laser diode)can be produced by forming a light emitting part comprising a claddinglayer and an active layer, and electrodes on the GaN group crystal basemember of the present invention, particularly, a GaN group crystal layer3 grown thick.

As in the embodiment of FIG. 1, when a low dislocation density part isformed on the mask layer 2, occurrence of dislocation is not reduced inother parts. Thus, in the present invention, as shown in FIG. 4, the GaNgroup crystal base member (base substrate 1, first mask layer 2 andfirst GaN group crystal layer 3) shown in the above-mentioned FIG. 1 isused as a new base substrate M, on which a second mask layer 21 isformed in the same manner as in FIG. 1, thereby shutting off extensionof the dislocation line, and then a second GaN group crystal layer 31 isgrown thereon. In this manner, a GaN group crystal base member almostwithout dislocation can be obtained. In FIG. 4, the dislocation lineslinearly rise from the non-masked region.

The GaN group crystal base member obtained by forming theabove-mentioned second GaN group crystal layer 31 is used as a new basesubstrate M, and a mask layer and a GaN group crystal layer may berepeatedly formed an optional number of times to form a GaN crystalhaving an almost non-dislocation state.

Another preferable mode for forming a mask layer is explained in thefollowing. When a dislocation line linearly advances upward from thenon-masked region, the GaN crystal of the part grown on the maskedregion is utilized. Thus, the masked region should be made as large aspossible. While a non-masked region which is unnecessarily large isuseless, too large a masked region has been found to be also undesirablein that the time necessary for the completion of the crystal growthbecomes long.

In the embodiment shown in FIG. 5, a mask layer 2 is formed on thesurface of a base substrate 1 to divide a masked region 12 from anon-masked region 11. The masked region 12 and non-masked region 11 areboth linear strips which are alternately formed in a periodic repeatpattern. The longitudinal direction of the linear strips of the maskedregion and non-masked region extends in the <1-100> orientation.

In the present invention, the preferable ranges are 1 μm≦B≦20 mm and 1μm≦A+B≦25 mm, wherein the width of the masked region (namely, stripwidth in <11-20> orientation) is B and the width of the non-maskedregion is A (strip width in <11-20> orientation, as in B).

The repeat pattern of the masked region and non-masked region may givestripes as shown in FIG. 5 or each strip may extend forming a certainangle with the <1-100> orientation. In either way, the masked region andnon-masked region form a regular repeat pattern in the <11-20>orientation as well.

The repeat pattern of the masked region and non-masked region may form azigzag line. Besides, a repeat pattern of strips forming an optionalcurves, such as sign curve, a repeat pattern concentrically forming anannulus ring or hexagon masked region, a coiled repeat pattern and thelike may be employed. Alternatively, a repeat pattern in which the ratioof A to B varies according to a certain relational formula may be used.

The width B of the masked region corresponds to the width of the lowdislocation density GaN group crystal to be grown thereon. A widthsuitable for use may be determined within said width, wherein it may beused as it is or divided before use. When B exceeds 20 mm, the GaN groupcrystal will require a long time to cover the masked region.Nevertheless, when B is less than 2 μm, a mask layer cannot be formedeasily, and the ratio of B to A+B becomes smaller to result in lessreduction of dislocation density of the GaN group crystal obtained.

When the dislocation line linearly advances upward from the non-maskedregion, the non-masked region is preferably as small as possible, sothat the limited area on the base substrate can be used most effectivelyand the largest possible area of the non-dislocation part is obtained athigh speed. It is preferable that the proportional relation of A and Bis always A≦B. It is more preferable to set the proportion of B to A+Bto 50%-99.998%, particularly 50%-99.98%. When the proportion of B to A+Bexceeds 99.998%, A becomes too small to prevent easy formation of thenon-masked region, and B becomes greater to require a large amount oftime for the GaN group crystal to cover the masked region.

The present inventors have further found that, when openings (non-maskedregion) are disposed on the mask layer, an orthogonal matrix formed bythe openings in the <1-100> orientation and <11-20> orientation as shownin FIG. 2 is associated with the following problem as shown in FIG. 8.

To be specific, as shown in FIG. 8(a), from the sides of the opening 4a, an off-facet plane 32 grows in the <11-20> orientation at high speedand a facet plane 31 grows moderately in the <1-100> orientation fromthe side extending in the <11-20> orientation. The off-facet plane isshown with a thick dotted line and the facet plane is shown with a thickline. Immediately after the crystal started growing from the opening inthe transverse direction on the mask layer, the transverse growth planescan be considered to be only two planes in the directions orthogonallycrossing with each other (e.g., FIG. 8(a), 31 and 32). As the growthproceeds, however, a facet plane 33 appears at the corner where theplanes 31 and 32 cross with each other.

A continued crystal growth results in enclosure of the central portion(vicinity of center point m) which is located at the same distance fromthe four openings 4 a, 4 b, 4 c and 4 d. It occurs at a certain point ofthe growth by the facet planes 33 a, 33 b, 33 c and 33 d slow in growth,as shown in FIG. 8(b).

Once it is enclosed solely by the facet planes slow in growth, theenclosed area (space) requires a long time to be closed by a continuedcrystal growth. During that long time period, the crystal continues togrow at high speed in the thickness direction (C axis orientation). Bythe time the enclosed area is filled, the thickness of the crystalbecomes unnecessarily great far exceeding the intended size. Inaddition, the central part (center point m) filled last consists of thecrystals from the four directions which are joined at one point, havinga low crystal quality with many defects.

In the present invention, therefore, the pattern formed by the openingsis set to be other than an orthogonal matrix formed by the openings inthe <11-20> orientation and <1-100> orientation, but parallelogram(exclusive of square and rectangle) or square without the side in the<11-20> orientation. In this way, the enclosure only by the facet planescan be avoided and at least one of the above-mentioned problems-can besolved. In particular, when, as shown in FIG. 7, the growth planes ofthe crystals gathered from respective openings enclose the central area,the position of the openings may be moved so that the central portionwill be enclosed by two facet planes and one off-facet plane, wherebythe remaining problems mentioned above can be entirely solved.

The problems solved in this way are the following.

a. High speed growth of off-facet plane enables filling of the enclosedarea in a short time.

b. The enclosed area is closed at an earlier stage relative to thegrowth in the thickness direction, so that a crystal having a desiredthickness can be obtained.

c. The portion closed last (center m) has a crystal structurecollectively formed by the crystals gathered from three directions, sothat the crystal quality can be improved as compared to the quality ofthe crystals from four directions. In addition, the enclosed area whichwas closed at an earlier stage continues to grow in the thicknessdirection, so that the crystal quality of said portion can be improvedduring the growth, and by the time the desired thickness is obtained,the surface layer of the crystal becomes far more improved in qualitythan it was when the area was closed.

In FIG. 6, on a base substrate 1 is formed a mask layer 2 (partiallybroken away in the Figure) and on the mask layer 2 are formed pluralopenings 4 in which the top surface of the base substrate 1 is exposedat the bottom. The pattern formed by the openings 4 at the top surfaceof the mask layer 2 is drawn by supposing a net having a quadrangle S1(shown in a thick line) as the minimum constituent unit, on the surfaceof the mask layer. The openings 4 are formed on the intersection of thenet lines. According to the present invention, this quadrangle S1 of thenet may be a parallelogram or a square or rectangle without the side inthe <11-20> orientation.

In the embodiment shown in FIG. 6, quadrangle S1 of the net is aparallelogram S1 formed by a part of the parallel two straight lines y1and y2 extending in the <1-100> orientation, as parallel two sides. Thepattern of the entire net supposed to be present on the surface of themask layer in the embodiment of FIG. 6 is a net wherein the parallelstraight lines y1 to y3 extending in the <1-100> orientation form anangle other than a right angle, namely, an angle θ1 (=one of interiorangles of parallelogram) with the parallel lines m1 to m3. The openingsnear the outer periphery may be increased or decreased in number by, forexample, omitting openings 4 e and 4 f, according to the outer shape ofthe substrate.

The net pattern may be, as shown in the embodiment of FIG. 6, completelycongruent parallelogram defined only by the parallel lines in twodirections, a pattern wherein mirror symmetrical parallelograms arealternately combined, a pattern wherein different parallelograms arecombined and the like.

The shape of the parallelogram constituting the net pattern ispreferably one wherein one of the two sides slides in the <1-100>orientation from the other side by half the length of said side. In theembodiment of FIG. 6, for example, it is a parallelogram wherein, of theopenings 4 a, 4 b, 4 c and 4 d at the four vertexes of theparallelogram, the sets (4 a, 4 c and 4 d) and (4 a, 4 d and 4 b) cometo the vertex of each isosceles triangle. The distance between theopenings in the <1-100> orientation is about 1 μm-10 μm, whereas that inthe <11-20> orientation along which the crystal grows at high speed isabout 2 μm-50 μm. These sizes can be determined by referring to thecrystal growth speed in the transverse direction.

Other embodiments of the net pattern include one wherein the minimumconstituent unit quadrangle of the net is a parallelogram having twoparallel sides extending in the <11-20> orientation, or a parallelogramincluding no straight line extending in the <1-100> orientation or<11-20> orientation, and the like.

As shown in FIG. 8(a), the plane 32 in the <1-100> orientation of thecrystal which grows from the opening decreases due to the growth of theoff-facet plane 33. In consideration of this, the shape of the openingis preferably one wherein the side in the <1-100> orientation has asufficient length. To be specific, it is a quadrangle having a sizefalling within the range specified by 10 μm-10 mm in the <1-100>orientation and 1 μm-10 μm in the <11-20> orientation, and having alonger side in the <1-100> orientation.

In the present invention, low dislocation density and high qualitycrystal formed on the masked region or non-masked region is utilized toform a GaN group semiconductor element using the low dislocation densitypart. In so doing, it is essential that the width of the masked regionand non-masked region be not less than the width of the active part ofthe element and not more than the width of the entire element. Forexample, when the part above the mask layer has a low dislocationdensity, the element is manufactured in such a manner that the maskedregion comes at least right beneath the active layer of the element. Inthis way, a high quality element can be ensured using the least possiblepart of the masked region.

When the mask layer forms a stripe pattern, GaN group semiconductorlayer is formed to give a laminate including a number of elements, andthe part above the mask layer has a low dislocation density, eachelement is preferably divided at the non-masked region. This obliteratesuseless breaking of high quality crystal parts when dividing theelements.

When an element is divided at a certain region, it is meant that aparting plane passes through said region and crosses the plane of eachlayer in a perpendicular relation.

While the element to be the production target is not particularlylimited, the element may be, for example, a light emitting element, alight receiving element, power device and the like. As the lightemitting element, exemplified are GaN group LED and GaN groupsemiconductor laser, and examples of power device include microwave FET,power MOSFET, HBT heterojunction bipolar transistor), MMIC (monolithicmicrowave integrated circuit) and the like.

The width of the element as exemplified by a light emitting element istypically those shown in FIG. 10. FIG. 10(a) shows a GaN group LEDhaving a GaN crystal as a substrate 1. The element as a whole is asimple rectangular parallelopiped wherein the width D of the element andthe width E of the active part k1 are the same. FIG. 10(b) shows a GaNgroup LED having a sapphire crystal as a substrate, wherein thesubstrate is an insulating member requesting the electrode disposed atthe upper side as shown in the Figure, and the width E of the activepart k1 is smaller than the width D of the element. FIG. 10(c) shows aGaN group stripe laser having a sapphire crystal as a substrate, whereinthe stripe structure necessitates the width E of the active part (stripepart) to be still smaller than the width D of the element, as comparedto the LED of FIG. 10(b).

In a stripe laser, the part to be the width of the stripe part variesaccording to the embodiment of the laser element. The width of thestripe part corresponds to the width of the member when the stripemember is embedded; the width of a laminate in an embodiment where thewidth of the laminate between two planes of resonators is narrowed tomake the shape of the laminate itself a stripe; and the width of anelectrode where the electrode is a stripe and the part of the activelayer, which comes beneath the electrode, becomes a stripe part. Theembodiment shown in FIG. 10(c) has a width E of the stripe part k1 whichis smaller than the width of the entire active layer.

The width of the element in FIG. 10 and the depth size of the element inthe direction perpendicular to the paper surface vary depending on thekind of element, inclusive of one having a large area (e.g., LED array).Typically, the size of a light emitting element such as a laser is aboutwidth 200 μm-500 μm and depth 200 μm-1000 μm per one element.

When the part above the masked region has a low dislocation density, asshown in FIG. 5, the width w1 between the two parallel straight lines p1and p2 extending in the <1-100> orientation should be equal to the widthof the production target element, particularly at least the widthcapable of being set beneath the active part. This enables efficient useof a high quality crystal above the masked region for an element, asshown in FIG. 9(b) and FIG. 11.

When the part above the masked region has a low dislocation density, itis preferable that a mask layer have two parallel straight linesextending in the <1-100> orientation which define the outer shape. Thewidth between the two straight lines need only be that allowable to comebeneath the active part, which may be selected from the range of fromthe width of the active part of the element to the width of the entireelement. In the case of a stripe laser, for example, since it has awidth selected from the range of from the width of the stripe (2 μm) tothe width of the entire element (1000 μm), the width of the maskedregion should be also 2 μm-1000 μm. In the case of an LED array having agreater area, at least the width of the masked region is set to fallwithin the range of from the width of the active part to the width ofthe entire element.

When the masked region forms a stripe as shown in FIG. 5 and elementsare formed above the masked region strips, a number of elements may beformed sequentially and integrally in the longitudinal direction aboveone masked region strip, and divided at a final stage. The width of thenon-masked region then may be any as long as the division is effected.In the element shown in FIG. 10(c), when the width of the masked regionand that of the active part are the same, the width of the masked regionbecomes minimum and that of the non-masked region at both sides thereofbecomes maximum.

When the part above the masked region has a low dislocation density, thenon-masked region becomes the starting point of the GaN group crystallayer growth as well as the cutting region for division. For example,when division utilizes braking, the width need only be that necessary asthe starting point of the crystal growth rather than the width necessaryfor division, since the division scarcely requires a loss width. Whenthe division involves the use of a diamond rotation blade, the lossshould be considered to be about 20 μm-50 μm.

From the above-mentioned aspects, the width of the non-masked region isselected from the range of from about 0.5 μm-5 mm, particularly fromabout 1 μm-1 mm, when a low dislocation density part is to be formedabove the masked region.

The method for manufacturing the element of the present invention asshown in FIG. 9(a), wherein the part above the masked region of the GaNgroup crystal layer has a low dislocation density, comprises growing asemiconductor layers k in such a manner that the active part comes atleast above the masked region and forming a laminate containing anecessary number of elements. In the embodiment shown in this Figure,the element is a simple GaN group LED wherein the width of the mask,that of the element and that of the active part are the same. The activepart which assumes the function of an element produces emission of lightand includes a pn junction. As shown in FIG. 9(b), the laminatecontaining the necessary number of elements is divided to separate eachelement. The base substrate may or may not be removed.

When the element is a stripe laser, it is preferably formed and dividedtaking note of the fact that the stripe portion extends in thelongitudinal direction and that the element contains a resonator.

For example, when the masked region forms a stripe as shown in FIG. 5and a low dislocation density part is formed above the masked region,the longitudinal direction of the part to be a stripe part is thelongitudinal direction of each masked region as shown in FIG. 11, andplural stripe lasers are efficiently formed in sequence above the maskedregion. With regard to the above-mentioned second point to be noted, theentire laminate is divided along the plane perpendicular to thelongitudinal direction of the stripe part, before division into eachstripe part (e.g., division along X1 and X2 in FIG. 11) to form a stringof adjoining elements in the <11-20> orientation as shown in FIG. 11.The end surface appearing on the plane of division of every strip istreated to make a reflector, and a resonator is integrally finished.Then, each GaN group stripe laser is efficiently separated by cuttingalong the plane parallel to the longitudinal direction of the stripepart (e.g., in FIG. 11, division along U1 to U4).

Conventionally, the dislocation line present in the GaN group crystallayer 3 has been considered to advance linearly in the thicknessdirection along with the growth of the layer, as shown in FIG. 1.Nevertheless, the present inventors have clarified that the dislocationline generated in the non-masked region can be freely led to the partabove the masked region or non-masked region by determining a mask layerpattern, crystal growth method and atmospheric gas during the crystalgrowth in combination. In other words, in the GaN single crystal layer 3in FIG. 1, any part above the masked region and non-masked region can bemade to have a low dislocation density.

In the present invention, as shown in FIG. 12(a) and FIG. 13(a), a masklayer 2 is formed on the base substrate 1 (wherein 12 is a masked regionand 11 is a non-masked region), and GaN group crystal is grown from thenon-masked region. In so doing, the ratio of the growth rate in the Caxis orientation (thickness orientation) of said GaN group crystal andthat in the orientation perpendicular to the C axis (transversedirection) is controlled to vary the crystal growth to the following (i)or (ii).

(i) When the growth rate in the C axis orientation is greater, themorphology of the surface upon crystal growth becomes that of a pyramidas shown in FIG. 12(b). In this way, the direction of the advancement ofthe dislocation line L can be bent toward the masked region side asshown in this Figure. Further crystal growth leads to joining of thecrystals from the adjacent masked regions as shown in FIG. 12(c), makingthe pyramidal top surface of the crystal layer flat. Along therewith,the dislocation line goes upward along the joining surface of thecrystals.

(ii) When the growth rate in the direction perpendicular to the C axisbecomes greater, the morphology of the surface upon crystal growthbecomes that of trapezoid having a flat top surface, as shown in FIG.13(b). In this way, the dislocation line L can be linearly led upward asshown in this Figure. Further crystal growth leads to joining of thecrystals from the adjacent masked regions as shown in FIG. 13(c), whileretaining the flat top surface only to increase the thickness of thecrystal layer. In this case, the dislocation line continues to goupward.

The controlling factors of the ratio of the above-mentioned growth ratein the C axis orientation and that in the orientation perpendicular tothe C axis are the pattern formed by the mask layer, crystal growthmethod and atmospheric gas during the crystal growth, and achievement ofthe above-mentioned crystal growth modes (i) and (ii) hinges on certaincombination of these factors.

For controlling the advancement direction of the dislocation line, thepattern of the mask layer is based on the direction of the boundary linebetween the masked region and non-masked region. As explained earlier,when the boundary line between the masked region and non-masked regionis a straight line extending in the <1-100> orientation, the off-facetplane grows in the transverse direction at a higher rate. As a result,the surface of the mask layer is covered while the GaN group crystallayer is still thin, as compared to the case of <11-20> orientation tobe mentioned next.

Conversely, when the boundary line between the masked region andnon-masked region is a straight line extending in the <11-20>orientation, the {1-100} plane, which is a facet plane, extends beyondthis boundary line into the transverse direction, making the growth ratein the transverse direction slower. Inasmuch as the growth rate in the Caxis orientation is higher than that in the transverse direction, slantfacet such as {1-101} plane tends to be formed. It necessitates makingthe plane flat after the pyramid plane is formed first. Consequently,the flat plane requires a certain thickness.

One example of the pattern showing the most noticeable effect of theabove-mentioned mask pattern is the stripe one shown in FIG. 5. Thelongitudinal direction of this strip is the direction of the boundaryline between the above-mentioned masked region and non-masked region.

Examples of the crystal growth method include HVPE, MOCVD and the like.When a thick film is to be manufactured, the HVPE method affording ahigher growth rate is preferred.

The atmospheric gas is exemplified by H₂, N₂, Ar, He and the like, andH₂ and N₂ are preferably used for controlling the dislocation line.

When the crystal growth is carried out in an H₂ rich atmospheric gas,the growth rate in the C axis orientation becomes higher. In particular,when the direction of the boundary line between the masked region andnon-masked region is a straight line in the <11-20> orientation, namely,slow in the transverse direction, the ratio of the rate in the C axisorientation becomes significantly greater, thereby making the crystalabove the non-masked region have a low dislocation density.

In contrast, when the crystal growth is carried out in an N₂ richatmospheric gas, the growth rate in the C axis orientation becomes lowerthan that when an H rich atmosphere is employed, as a result of whichthe growth rate in the transverse direction becomes relatively greater.When the growth rate in the transverse direction is accelerated by thecombination with the mask pattern, the crystal above the masked regioncomes to have a low dislocation density, as shown in FIG. 13.

The crystal growth by MOCVD is mainly carried out under an H₂ richatmosphere. For example, when a combination of carrier gas hydrogen (10L)+hydrogen gas (100 cc) for organic metal bubbling as a III group gasand carrier gas hydrogen (5 L)+ammonia (5 L) as a V group gas are used,a hydrogen concentration is 75%, which is one example of H₂ richatmosphere having 0% nitrogen concentration.

On the other hand, in N₂ rich atmosphere in the case of theabove-mentioned MOCVD crystal growth, the nitrogen concentration whenthe III group carrier gas is changed to nitrogen is about 50%. When theV group carrier gas alone is changed to nitrogen, the nitrogenconcentration is about 25%. Thus, a gas having a nitrogen concentrationof not less than about 25% is designated to be N₂ rich.

The part of the GaN group crystal having a low dislocation density whichis obtained by intentionally avoiding the passage of the dislocationline is positioned at the center of a light emitting part of a lightemitting layer, so that a preferable light emitting element as shown inFIGS. 14 and 15 can be obtained.

The element shown in FIG. 14 is one embodiment of the GaN group LED ofthe present invention, wherein, in the active layer 5 of the element,the part above the non-masked region has a low dislocation density. Thispart having a low dislocation density is the center of the lightemission due to a current stricture structure. In contrast, in theactive layer 5 of the element of the GaN group LED shown in FIG. 15, thepart above the masked region has a low dislocation density and is thecenter of the light emission.

When the preferable conditions to grow the GaN group crystal faster inthe transverse direction are not known, the GaN group crystal hasgreatly grown in the thickness direction as well when the GaN groupcrystal has completely covered the mask layer, which inevitablyincreases the thickness T from the top surface of the mask layer to thetop surface of the GaN group crystal layer. When the width W of the masklayer is reduced, however, the GaN group crystal quickly covers the masklayer completely, thereby making the thickness T smaller. Inconsequence, the ratio of the thickness T from the top surface of themask layer of the GaN group crystal layer to the width W of the masklayer, T/W, cannot become smaller than a certain level. This in turn hasresulted in the problem that a GaN group crystal layer formed on asufficiently wide masked region inevitably becomes thick and isassociated with cracks and warping.

The smallest ratio T/W heretofore reported is 1.75 wherein the width Wof the mask layer is that in the <11-20> orientation, and T=7 μm whenW=4 μm.

The present invention suggests, as stated with respect to the method forcontrolling the direction of the above-mentioned dislocation line, thatthe pattern of the mask layer be such having the boundary line betweenthe masked region and non-masked region extending in the <1-100>orientation, the GaN group crystal be grown by MOCVD (Metal OrganicChemical Vapor Deposition) and the atmospheric gas in which the GaNgroup crystal is grown by the MOCVD be an N₂ rich gas. When these threerequirements are fulfilled, the ratio of the thickness T of the GaNgroup crystal layer 3 covering the mask layer 2 formed on the basesubstrate 1 to the width W of the mask layer 2 in the <11-20>orientation, T/W, becomes not more than 1.75, whereby a thin GaN groupcrystal layer conventionally unattainable as shown in FIG. 16 can beobtained.

The present invention is described in more detail in the following byway of illustrative Examples and Comparative Examples, which are not tobe construed as limiting the present invention.

EXAMPLE 1

A 20 nm thick AlN buffer layer was grown at a low temperature using aMOVPE device on a sapphire substrate (C face) having a diameter of 2inches and a thickness of 330 μm, and a 1.5 μm GaN thin layer was grownthereon to give a base substrate. An SiO₂ thin film having a thicknessof 500 nm was formed as a masking material on the surface of thissubstrate by a sputtering method, and a mask layer was formed by leavingthe mask material in a lattice pattern at a line width of 100 μm and 200μm pitch by etching. That is, 100 μm square exposed parts were arrayedat 200 μm intervals. This new substrate was set in an HVPE device togrow 300 μm thick n-type GaN layer. The mask layer was completelyembedded, wherein the surface flatness was fine, and a 2 inch diametern-type GaN group crystal base member was obtained.

The GaN on the mask layer was evaluated by TEM. As a result, thedislocation density was not more than 1×10² cm⁻².

EXAMPLE 2

Using the same manufacturing method as in Example 1, a 50 nm thick AlNbuffer layer and a 1.5 μm GaN thin layer were grown on a sapphiresubstrate (C face) having a diameter of 2 inches and a thickness of 330μm to give a base substrate. The mask pattern was a stripe wherein 500nm thick, 200 μm wide linear SiO₂ mask layers and 200 μm wide exposedparts were alternately disposed. The longitudinal direction of thestripe was the <1-100> orientation. This was set in an HVPE device togrow a 220 μm thick n-type GaN layer. The mask layer was completelyembedded without occurrence of cracks, whereby a 2 inch diameter n-typeGaN group crystal base member having fine surface flatness was obtained.

EXAMPLE 3

In the same manner as in Example 1, a mask layer having a latticepattern and an n-type GaN layer were grown on a base substrate. A secondmask layer having the same lattice pattern as in Example 1 was grown onthis n-type GaN layer. This second mask layer covered right above thenon-masked region. This was set in an HVPE device to grow a 300 μm thicksecond n-type GaN layer.

The second n-type GaN layer thus obtained was evaluated by TEM. As aresult, the dislocation density was not more than 1×10² cm⁻².

EXAMPLE 4

A mask layer made from an SiO₂ thin film was formed by a sputteringmethod so that a linear strip pattern as shown in FIG. 5 was drawn onthe surface of the base substrate similar to that used in Example 1 togive a substrate for growth. The mask layer was formed to have stripsextending in the <1-100> orientation. The proportion of B to A+B was90.9% where the thickness was 0.5 μm, strip width (=width B of maskedregion) was 100 μm and intervals between strips (=width A of non-maskedregion) was 10 μm.

A GaN crystal was grown on this substrate for growth by an HVPE deviceat a 50 μm/hr growth rate for 4 hr to give a 200 μm thick GaN crystallayer. The dislocation density of the GaN crystal grown on the maskedregion was evaluated by TEM. As a result, the dislocation density wasnot more than 1×10⁴ cm⁻². The sapphire substrate was removed by abrasionto give a flat GaN crystal substrate.

EXAMPLE 5

A 25 μm thick GaN crystal was grown under the conditions wherein thewidth B of the masked region was 1 μm, the width A of the non-maskedregion was 1 μm and the proportion of B to A+B was 50%.

As a result of the processing in this Example, it has been found thatsetting the width B of the masked region to less than 1 μm istechnically difficult. It has also been found that reduction of thedislocation density becomes small unless B/(A+B) is large, which in turncauses noticeable problems of significantly reduced crack preventioneffect, thereby reducing the advantageous effects of the presentinvention.

EXAMPLE 6

A 11 mm thick GaN crystal was grown in the same manner as in Example 1under the conditions wherein the width B of the masked region was 20 mm,the width A of the non-masked region was 0.5 μm and the proportion of Bto A+B was 99.998%.

The sapphire substrate was removed by abrasion to give a GaN singlecrystal substrate which was a thick, bulky and flat crystal having awide area. The irregularities on the surface were somewhat greater thanthose found in Examples 1 to 3.

It has been clarified from this Example that the width of the maskedregion should be 20 mm at the greatest. When the width of the maskedregion is greater than this, the time necessary for the step becomeslonger and the surface morphology tends to be degraded. As a result ofthe processing wherein the width A of the non-masked region was 0.5 μm,it was found that the width A of less than 0.5 μm was difficult toachieve. Thus, the proportion of B to A+B is preferably about 99.998% atthe greatest.

EXAMPLE 7

A 11 mm thick GaN crystal was grown in the same manner as in Example 1under the conditions wherein the width B of the masked region was 20 mm,the width A of the non-masked region was 5 mm and the proportion of B toA+B was 80%. As a result, the GaN crystal layer contained numerouscracks extending from the non-masked region to the masked region. Thus,a greater width of the non-masked region was not desirable due to theoccurrence of cracks, and the upper limit of A was 5 mm.

EXAMPLE 8

An SiO₂ mask layer was formed on the surface of the base substratesimilar to that used in Example 1. Then, openings were formed by etchingto give a substrate for growth of the type shown in FIG. 6. The shape ofthe openings was congruent, which was a rectangle having the size of<11-20> orientation 3 μm×<1-100> orientation 100 μm.

The pattern of the disposed openings was such that the width of themasked region sandwiched between the adjacent openings was 5 μm in the<11-20> orientation and 2 μm in the <1-100> orientation, and the shapeof parallelogram of the net pattern was such that one of the two sidesin the <1-100> orientation slid by a half of the length of the side inthe <1-100> orientation.

The above-mentioned substrate for growth was set on an HVPE device, anda 200 μm thick GaN group crystal layer was formed from the non-maskedregion as the starting point. The GaN group crystal grew on the masklayer in the transverse direction as well to completely cover the masklayer.

The flatness of the GaN group crystal layer surface was fine. The partformed by the crystals that grew in the transverse direction and joinedfrom each opening further grew in the thickness direction after thejoining. The surface layer and the vicinity thereof had fine crystalquality.

EXAMPLE 9

In this Example, the objective element to be formed was a stripe laser.As shown in FIG. 5, the mask layer was a parallel stripe extending inthe <1-100> orientation of GaN crystal. The substrate for growth wasprepared in the same manner as in Example 1, wherein the pattern of themask layer was width 150 μm and the central pitch 300 μm.

Stripe Laser Structure

A 100 μm GaN crystal layer was formed on the substrate for growth togive a substrate, on which were sequentially grown in its entirety n-GaNlayer/n-AlGaN layer/n-GaN layer/InGaN multi-quantum well layers/p-AlGaNlayer/p-GaN layer/p-AlGaN layer/p-GaN layer. The laminate was etched byRIE (Reactive Ion Etching) leaving 8 μm width strips to give a stripelaminate as shown in FIG. 11 by k. The stripe was aligned with the aboutcenter of the mask layer, so that the stripe could be in the <1-100>orientation. Abrasion removed the sapphire substrate (C face) to makethe entire thickness 80 μm.

Division Into Each Element

Cleavage along the plane orthogonally crossing the longitudinaldirection of the stripe as the parting plane, namely, cleavage along X1and X2 in FIG. 11 and at 500 μm pitch in parallel relation thereto(cleavage at M plane), gave a number of elements in sequential adjacencyin the <11-20> orientation. A necessary coating was applied to thereflector surface thereof at once to finish the resonator. Then, theelements were separated along U1 to U4 in FIG. 11 to give respectivelaser chips.

This Example confirmed efficient forming of elements by aligning themasked region with the stripe part. In addition, by determining thestripe direction and by the above-mentioned steps of division, efficientproduction of stripe lasers was attained.

EXAMPLE 10

As shown in FIG. 12, the dislocation line was bent to the part above themasked region to make the part above the non-masked region a lowdislocation density part.

Base Substrate

As the most basic crystal substrate, used was a sapphire substrate (Cface). On the surface thereof, an AlN low temperature buffer layer andGaN layer were grown to the thickness of 2 μm to give a base substrate.

Mask Layer

The substrate was taken out from the growth apparatus and an SiO₂ masklayer was formed by sputtering. The pattern of the mask layer was astripe wherein the longitudinal direction of the strip was the <11-20>orientation of the GaN group crystal to be grown.

Growth of GaN Group Crystal; Completion of Base Member

Then, this specimen was placed in an MOCVD device and heated to 1000° C.under a hydrogen atmosphere containing ammonia. TMG and ammonia wereflown for 30 min to grow GaN crystal. The GaN crystal first grew in apyramid shape as shown in FIG. 12(b), and the dislocation line was benttoward the masked region side. The crystal was further grown until itbecame flat at 10 μm.

Light Emitting Element

As shown in FIG. 14, a current blocking layer 6 was formed in such amanner that the low dislocation density part came to the light emittingcenter of the light emitting layer 5 to form a light emitting element.As a result, one having a high light emission efficiency was prepared.In FIG. 14, 7 is an upper cladding layer and 8 and 9 are electrodes.

EXAMPLE 11

In the same manner as in Example 1 except that the mask layer stripe hada longitudinal direction which was the <1-100> orientation of the GaNgroup crystal to be grown and the atmospheric gas was nitrogen rich, aGaN group crystal layer was formed. The thickness until it became flatwas 2 μm.

As shown in FIG. 15, thereafter, a current blocking layer 6 was formedin such a manner that the low dislocation density part came to the lightemitting center of the light emitting layer 5 to form a light emittingelement. As a result, a light emitting element having a high lightemission efficiency was obtained. As in FIG. 14, 7 is an upper claddinglayer and 8 and 9 are electrodes.

EXAMPLE 12

In this Example, a thin GaN crystal was formed.

Base Substrate

As the most basic crystal substrate, used was a sapphire substrate (Cface). On the surface thereof, an AlN low temperature buffer layer andGaN layer were grown to the thickness of 2 μm to give a base substrate.

Mask Layer

An SiO₂ mask layer was formed by sputtering. The pattern of the masklayer was a stripe wherein the longitudinal direction of the strip wasthe <1-100> orientation of the GaN group crystal to be grown. The widthof the strip of the non-masked region was 4 μm and the width W of thestrip of the masked region was 4 μm.

Growth of GaN Crystal; Completion of Base Member

Then, this specimen was placed in an MOCVD device and heated to 1000° C.under a nitrogen rich atmospheric gas (III group carrier gas nitrogen(10 L), gas (100 cc) for organic metal bubbling, V group carrier gashydrogen (5 L), ammonia (5 L)). TMG and ammonia were fed to grow GaNcrystal. The GaN crystal at the point the surface of the mask layer wascompletely embedded had a thickness T of 2 μm, as shown in FIG. 16.Thus, T/W was 0.5.

Comparative Example 1

In the same manner as in Example 1 except that the atmospheric gas waschanged from nitrogen rich to hydrogen rich, a GaN crystal was grown.The GaN crystal at the point the surface of the mask layer wascompletely embedded had a thickness T of 7 μm. Thus, T/W was 1.75.

Comparative Example 2

In the same manner as in Example 1 except that the atmospheric gas waschanged from nitrogen rich to hydrogen rich and the longitudinaldirection of the stripe of the mask layer was the <11-20> orientation, aGaN crystal was grown. The GaN crystal at the point the surface of themask layer was completely embedded had a thickness T of 12 μm. Thus, T/Wwas 3.

What is claimed is:
 1. A GaN group crystal base member comprising a basesubstrate, a mask layer for controlling an extension of dislocation linepartially covering the surface of said base substrate to give a maskedregion, and a GaN group crystal layer grown thereon to cover said masklayer, which is partially in direct contact with a non-masked region ofthe base substrate, wherein the base substrate has at least a surfacelayer represented by the formula: In_(x)Ga_(y)Al_(z)N wherein 0≦X≦1,0≦Y≦1, 0≦Z≦1, X+Y+Z=1.
 2. A GaN group crystal base member comprising abase substrate, a mask layer for controlling an extension of dislocationline partially covering the surface of said base substrate to give amasked region, and a GaN group crystal layer grown thereon to cover saidmask layer, which is partially in direct contact with a non-maskedregion of the base substrate, wherein the GaN group crystal layer is afirst GaN group crystal layer, which further comprises a second masklayer partially covering the surface of said first GaN group crystallayer and a second GaN group crystal layer grown thereon to cover thesecond mask layer, which is partially in direct contact with anon-masked region of the first GaN group crystal layer.
 3. A GaN groupcrystal base member to be used as a crystal substrate of a GaNsemiconductor element, comprising a base substrate, a mask layer forcontrolling an extension of dislocation line partially covering thesurface of said base substrate to give a masked region, and a GaN groupcrystal layer grown thereon to cover said mask layer, which is partiallyin direct contact with a non-masked region of the base substrate,wherein the base substrate permits growth of a GaN group crystal in theC axis orientation as the thickness direction, and the mask layer ismade from a material substantially free from GaN group crystal growth,and wherein the GaN crystal layer has grown to cover the mask layer froma non-masked region as the growth starting point, and the mask layerforms a pattern wherein the width of the part having a low dislocationdensity within said crystal exceeds the width of an active part of saidGaN group semiconductor element.
 4. The GaN group crystal base member ofclaim 3, wherein a masked region and a non-masked region are alternatelyrepeated periodically, said periodic repetition comprising at least arepetition in a <11-20> orientation of the GaN group crystal to be grownon said base substrate, a width B of said masked region in the <11-20>orientation and a width A of said non-masked region being defined by 1μm≦B≦20 mm and 1 μm<A+B≦25 mm.
 5. The GaN group crystal base member ofclaim 3, wherein the mask layer has plural openings on the surfacethereof, the base substrate being exposed at the bottom of the openings,an arrangement pattern of said openings on the surface of the mask layerbeing one wherein the openings are positioned at intersections of netlines forming a quadrangle as the smallest constituent unit, saidquadrangle being a square without a side in the <11-20> orientation ofthe GaN group crystal to be grown on the base substrate, orparallelogram.
 6. The GaN group crystal base member of claim 3, whereinthe ratio of a thickness T of the GaN group crystal layer covering themask layer from the mask layer surface to a width W of the mask layer inthe <11-20> orientation is T/W<1.75.
 7. The GaN group crystal basemember of claim 3, wherein the GaN group semiconductor element is a GaNgroup light emitting diode.
 8. A GaN group crystal base member to beused as a crystal substrate of a GaN semiconductor element, comprising abase substrate, a mask layer for controlling an extension of dislocationline partially covering the surface of said base substrate to give amasked region, and a GaN group crystal layer grown thereon to cover saidmask layer, which is partially in direct contact with a non-maskedregion of the base substrate, wherein the base substrate permits growthof a GaN group crystal in the C axis orientation as the thicknessdirection, and the mask layer is made from a material substantially freefrom GaN group crystal growth, and wherein a masked region having, asouter shape lines, two parallel straight lines extending in the <1-100>orientation of the GaN group crystal to be grown on said base substrate,and the width between the two straight lines being not more than thewidth of said GaN group semiconductor element and not less than thewidth of an active part of said element.
 9. The GaN group crystal basemember of claim 8, wherein a masked region and a non-masked region arealternately repeated periodically, said periodic repetition comprisingat least a repetition in a <11-20> orientation of the GaN group crystalto be grown on said base substrate, a width B of said masked region inthe <11-20> orientation and a width A of said non-masked region beingdefined by 1 μm≦B≦20 mm and 1 μm<A+B≦25 mm.
 10. The GaN group crystalbase member of claim 8, wherein the mask layer has plural openings onthe surface thereof, the base substrate being exposed at the bottom ofthe openings, an arrangement pattern of said openings on the surface ofthe mask layer being one wherein the openings are positioned atintersections of net lines forming a quadrangle as the smallestconstituent unit, said quadrangle being a square without a side in the<11-20> orientation of the GaN group crystal to be grown on the basesubstrate, or parallelogram.
 11. The GaN group crystal base member ofclaim 8, wherein the ratio of a thickness T of the GaN group crystallayer covering the mask layer from the mask layer surface to a width Wof the mask layer in the <11-20> orientation is T/W<1.75.
 12. The GaNgroup crystal base member of claim 8, wherein the GaN groupsemiconductor element is a GaN group stripe laser, the width of saidactive part is the width of a stripe part in the stripe laser, and thedirection of the extension of the two parallel lines is the longitudinaldirection of the stripe part in the stripe laser.